#include <bits/stdc++.h> #pragma GCC optimize("Ofast") #define _GLIBCXX_DEBUG using namespace std; using std::cout; using std::cin; using std::endl; using ll=long long; using ld=long double; ll ILL=2167167167167167167; const int INF=2100000000; const ll mod=998244353; #define rep(i,a) for (ll i=0;i<a;i++) #define all(p) p.begin(),p.end() template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>; template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();} template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();} template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;} template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;} template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());} template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});} void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";} template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";} void solve(); // oddloop int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int t=1; //cin>>t; rep(i,t) solve(); } void solve(){ ll N; cin>>N; ll l=0,r=N-1; while(r-l>1){ ll med=(l+r)/2; ll R=3*med+1-N-N+1,S=N-2; //cout<<R<<endl; while(S>med&&R>0){ ll A=2*S+2-1-2*R; S--; R-=A; } if(R<=0) l=med; else r=med; } cout<<l<<"\n"; }